The LM25116 contains an enable function allowing a very low input current shutdown. If the enable pin is pulled below 0.5 V, the regulator enters shutdown, drawing less than 10 µA from the VIN pin. Raising the EN input above 3.3 V returns the regulator to normal operation. The maximum EN transition time for proper operation is one switching period. For example, the enable rise time must be less than 4 µs for 250-kHz operation.

A 1-MΩ pullup resistor to VIN can be used to interface with an open collector control signal. At low input voltage the pullup resistor may be reduced to 100 kΩ to speed up the EN transition time. The EN pin can be tied directly to VIN if this function is not required. It must not be left floating. If low-power shutdown is not required, the UVLO pin must be used as an on/off control.

Figure 6-3 Enable Circuit

Figure 6-4 EN Bias Current vs Voltage